Electron discharge device of the cavity resonator type



C. T. GODDARD ELECTRON DISCHARGE DEVICE OF THE CAVITY RESONATOR TYPEApril 14, 1953 Flled Dec 1, 1950 April 14, 1953 c. T. GODDARD ELECTRONDISCHARGE DEVICE OF THE CAVITY RESONATOR TYPE 2 SHEETS-SHEET 2 FiledDec. 1, 195o /N VEN To@ '6. 7.' GOOD/IRD A 7' TORNEI( Patented Apr. 14,1953 ELECTRON DISCHARGE DEVICE OF THE CAVITY RESONATOR TYPE charles r.Goddard, Basaing Ridge, N. J., assigor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationDecember 1, 1950, Serial No. 198,612

8 Claims.

This invention relates to electron discharge devices and, moreparticularly, to reflex oscillators of the cavity resonator type.

The trend of design in such reflex oscillators has been consistently tosmaller wavelengths. The attainment of eliicent and satisfactoryopjeration at extremely high frequencies and short wavelengths requiressmaller dimensioned electrodes and very close spacings between theelectrodes and between the electrodes and the other' an illustrativedevice being of the order of .023

inch. In order thatan advantageously high percentage of electronsemitted by the cathode may pass through this small area, the electrodeswhich comprise the cathode gun assembly must be accurately aligned andbe positioned within very close requirements. This requires the criticalspacing and alignment of the cathode surface, the beam electrode, andthe focusing electrode. Any rotational inaccuracy, such as a tilt ofeven one degree, in the cathode or any displacement of the cathode orthe beam electrode, such as of the order of .003 or .005 inch, from theaxial alignment of the focusing electrode will considerably reduce thepercentage of emitted electrons directed through the small aperture intothe cavity resonator.

It is, therefore, one object of this invention that a very highpercentage of electrons emitted from the cathode shall pass through theextremely small vaperture required for very high frequency operation andshall enter into the cavity resonator.

A further object of this invention is to accurrately align and positionthe electrodesy and elements of the electron gun assembly required fordevices intended for extremely high frequency operation.

A further object of this invention is to reduce the number ofdimensional tolerances introduced into the alignment and positioning ofthe elements of the electron gun assembly and, more particularly, toreduce the number of tolerances that must be accurately kept on any oneof these elements.

A still further object of this invention is to facilitate theassemblying of the electron gun and, more particularly, to do so byeliminating the use of assembling jigs and the concomitant introductionof dimensional errors because of the tolerances inherent in the jigsthemselves.

These and other objects of this invention are attained in one specificillustrative embodiment wherein the focusing electrode is provided withan accurately determined external diameter and a ridge internal to thatdiameter and extending further along the axis of the electrode. Aninsulating ring of precise thickness surrounds this ridge and ts looselyon the focusing electrode. A larger insulating member with an accuratelydetermined inner diameter ts snugly over the accurately determinedexternal diameter of the focusing electrode. A beam or beam formingelectrode is provided with a plurality of thin lingers fitting directlyonto the cathode sleeve to which the other portions of the cylindricalbeam electrode are adjacent. The cathode sleeve diameter and the innerdiameter of the cylindrical beam electrode are accurately determined.The beam electrode fits into the accurately determined inner ring of thelarger insulator, the outer diameter of the beam electrode fittingsnugly into the insulator ring. Spring means bear againstthe beamelectrode and bias it towards the focusing electrode. In thisembodiment, the various components of the electron gun assembly are thusall supported by each other in a single unit.

It is, therefore, one feature of this invention that each of thecomponents of the electron gun assembly positions and aligns othercomponents of the assembly without the use of external jigging oraligning means.

i It is a further feature of this invention that the required toleranceson each component part f the electron gun assembly are reduced to aminimum and, more particularly, that each part has only a singlecritical dimension, which may be accurately determined in the machiningof the parts.

It is a further feature of this invention that the beam formingelectrode is secured directlyto the cathode by means of a plurality ofthin fingers, the beam electrode thus supporting the cathode inthecathode gun assembly. Further, as the only thermal contact between thetwo is made by these fingers extending onto the cathode sleeve, the beamelectrode can be maintained cooler than the cathode.

It is a further feature of this invention that all of the components ofthe electron gun assembly are supported together as a single unit by asingle retaining means. A

It is a still further feature of this invention that the components ofthe electron gun assembly are maintained in proper position by. springmeans. 1

A complete understanding of this invention and of the various featuresthereof may be gained from consideration of the following detaileddescription and the accompanying drawings, in which:

tioning of the elements of the electrongun'are substantially reduced.This can best be seen by reference to Fig. 3 and to one advantageousprocedure of assembling the component parts of the unitary electron gunassembly, which will also demonstrate the facility with which theelectron gunassembly can be commercially assembled under large scaleproduction conditions.

The small insulator ring 31 is advantageously first dropped around thecircular ridge 3l on the focusing electrode 28. The large insulator ring36 may then be dropped around the portion 30 of the focusing electrode28, the ring 36 fitting closely around the outer surface 29 of theportion 30. The beam electrode 38 is secured as by welding at thefingers to the cathode sleeve 42, the fingers 39 extending along thesleeve and supporting it. The main body of the beam electrode 38 itselfis, however, advantageously not in contact with the sleeve 42, asexplained more fully below. The beam electrode 38 to which the cathodesleeve 42 is attached is then advantageously placed into the centralaperture in the large insulator ring 36, the inner edge of the beamelectrode 38 resting on the small insulator ring 31 which accuratelypositions it from the focusing electrode 25. As this central aperture inthe large insulator ring 36 has been accurately machined or otherwisedimensioned to fit closely over the surface 29 of the portion 30 of thefocusing electrode 28, the beam electrode 38 is accurately positioned inaxial alignment with the focusing electrode 28. The springs 48 and 5|,with theintervening insulator ring 50,

are then positioned in place, and the assembly locked by bending overaplurality of the iingers 52 of the retaining member 53.

`It is to be particularly noted that not only is no external jiggingrequired to center or position any of the components of the gunassembly, but further that none of the elements are welded or otherwisepermanently secured to another element, except thatthe beam electrodefingers 39 may advantageously be welded to the cathode sleeve 42.However, the fingers 39 are so short that any deformation from thiscause is minimized. This obviates the appearance of any stresses in theassembly due to the welding, or

.other securing operations, which could be poit is highly desirable thatthe possibility of rejection of a device as not meeting the requiredcommercial standards for these causes be reduced.

The cathode sleeve 42, as discussed above, advantageously is held onlyby the fingers 39. As

the cathode sleeve is thus held adjacent the` emitting surface 43 by aplurality of fingers extending along the outer surface of the sleeve,

the possibility of objectionable tilting of the cathode surface 43 isgreatly reduced. Further by accurately dimensioning the outer surface ofthe cathode sleeve 42 and the inner surface of the beam electrode 38, i.e., of the electrode and liu its fingers 39, axial alignment of thecathode sleeve 42 with the focusing electrode 28 is also assured.

The beam electrode 38 is advantageously of Ni1var, a nickel-iron alloy,or other metallic material having a low thermal conductivity, While thespider spring 43 is advantageously of a nickelchromium-iron alloy knownas Inconel X,stain less steel, or other metallic spring material havinga higher thermal conductivity. By positioning the beam electrode 38 awayfrom the cathode sleeve 42 to which it is only connected by the fingers3S, heat is conducted to the beam electrode 38 only through the fingers39. However, because of the relative thermal characteristics of the beamelectrode 38 and the spider spring 48 this heat seeps away through thebeam electrode iianges 40 to the spring and to the insulator 36 so thatthe beam electrode 38 itself remains relatively cool.

An idea of the dimensions involved in a specic embodiment of thisinvention employable in -a device operable at wavelengths of the orderof 6 millimeters can be obtained from the following dimensions, whichare, of course, only exemplary:

Inner diameter of ring 36--. .142 i .0005 inch Thickness of ring 31 .019i .001 inch Diameter of cathode sleeve 42 .125 i .001 inch Outerdiameter of focusing electrode portion 30 .140 i .0005 inch Inaccordance with one desirable feature of this invention, as discussedabove, the other dimensions of these elements are not critical, therebyYmaking possible the accurately aligned electron gun assembly inaccordance with this invention.

It is to be understood that the above-describedl cathode sleeve adjacentsaid emitting surface, a`

focusing electrode, the outer surfaces of said beam electrode and saidfocusing electrode being aligned, insulating means closely fittingaround said aligned outer surfaces and positioning said cathode sleeve,beam electrode, and focusing electrode in axial alignment, and meanslocking said electrodes and said insulating means in a unitary assembly.

2. An electron gun assembly comprising "a cylindrical cathode sleevehaving an electron emitting surface at one end, a beam electrode havinga plurality of fingers extending along said cathode sleeve adjacent saidemitting surface,

, a focusing electrode, the outer surfaces of said beam electrode andsaid focusing electrode being aligned. first insulating means closelyfitting around said aligned outer surfaces and positioning said cathodesleeve, beam electrode, and focusing electrode in axial alignment,second insulating means coaxial with said beam and focusing electrodesand insulating said electrodes from each other, spring means biasingsaid lbeam electrode towards said focusing electrode, and means lockingsaid spring means, said electrodes, and

said* insulating means in' a', compact' unitaryV assembly.

3. An electron gun assembly comprising.l ai

cylindrical cathode sleevey having anl electron. emitting surface atyoneend, a' beam` electrode positionedadjacent saidone end andzcoaxial withs-aidfsleeve, said-beam electrodehaving: a plurality, of .short lingersextending along said sleevev andfcomprising" the only contact betweensaid:

beam electrode andzsaid sleeve, .a focusing electrode' coaxial with saidbeam'electrode; the outer surfacesof saidy focusing electrode and ,saidbeamV electrodebeing aligned,l an insulatorring closely fitting aroundsaid aligned outer surfacesrv and` positioning said cathodesleeve,bearnxelectrode,

andV focusing-` electrodex in axialalignment, andiv means'locking saidelectrodes and said insulating means .in-a :compact unitary assembly;

415A electron discharge device comprising@ a. cylindrical cathode sleevehaving an electron.

emittingsurface atfone end, a beam electrode positioned adjacentsaid oneend and c'oaxial with said-cathode sleeve, said beam electroderhaving a'plurality-of 'ngers extending along said sleevef and* comprising the.only` contact :between said beam electrode and said sleeve, a focusingelectrode coaxial'with said beam electrode, the outer` surfacesof saidfocusing electrode Iand saidbeainelectrode being aligned, a Firstinsulator ring closely fitting around said aligned outer surfaces andpositioning said cathode sleeve, beam electrode, and: focusing electrodein axial alignment, a second insulator ring positioned within said rstring and substantially coaxial therewith, said secon'dgring'beingbetween saidfbearn and said focusing electrodes, spring meansfbiasingsaidr beam4 electrodetowards said focusing electrode, and meanslockingsaid spring means, said'electrodes, and said insulator` rings in acompact unitaryassembly'.l

An` electron discllargey device comprisingl aA focusing electrode havinga cylindrical portion, a circular ridge extending from said portion andcoaxial therewith, a first insulator ringy positioned around-said ridge,a cylindrical beam electrode bearing against said first ring andhavingjtheisame outer diameter assaid portion, said beam electrodehaving a plurality of fingers extendingV therefrom Vandangesgintermediate,said fingers, a cylindrical cathode` sleeve adjacentsaid beam electrode, Asaidcathode sleeve havingv an felectronemitting'surface positioned towards said" focusing electrode, saidfingers extending along said cathode sleeve, a second insulator ringclosely encompassing said'portion and said beam electrode andpositioningsaid electrodes and said` focusing electrode positionedin said apertureand.

secured to said mounting member, said focusing electrode having acylindrical portion extending behind said mounting member, a circularridge coaxial with said cylindrical portion and extending. therefrom, afirst insulating ring positioned around saidcridge,a'fhollowfrcylimirical beam eleca trode bearingagainstisaidfirst:insulatorzring'sandf. coaxial with, said;v cylindrical; portion,Vthe;`A outen surfaces;l ofi saidi cylindrical: portion and saidf beameleotroderbeing aligned, aacylindrical cath--v ode sleevehavinganelectronemissive surface ad`- jacent said-beam electrode,- said beamvelectrode;z having axpluralityiof .1 integral ,fingers extending` alongsaid cathode sleeve and integral flangesin-i termediatea said fingers,a: secondiinsulatorring ittingw closely around: saidl aligned` surfaces.and positioningv said'V cathode sleeve, said; beam electrodeand saidfocusing. electrode inaccurate axial alignmentgv. spring. means "bearingagainstA said'flanges and biasing saidV beam electrode to.- Wardssaidrfccusingaelectrode,v and a cylindrical." retainingmember `securedto said mountingmeme berf and encompassingsaid'y 'second insulator ring;said `retaining.'member 5 having fingers bent over,` andexerting'pressure;uponv but insulated from said springineans.`

7'. Any velectron'v discharge: devicev in accord;-v

ancezwithgclaim 6 vwherein vsaid beam electrode;-A

fingers compriseathefonly. thermal contactbe.a4 tween;,said cathodesleeve* and said'beam elec trode';

8. An' electron dischargefdevice comprisingr'ai mounting vmember` havingan aperture therein,. a focusing electrode positioned inA saidAaperture' and isecured` to said? mounting member, .a cavity: resonatorApositioned rto one side ofi said mounts. ing` member; saidtfocusing'lelectrode havingA an* aperture defining an entrance for electrons intosaidi resonator, va cylindricali portion' extending' fron-[said focusingelectrode away from said' resi-- onator; saidcylindrical ,por-tion'having a .circular ridge, a yfirst insulating ring having an accurately`determined thickness: positioned loosely around: said ridge, a hollowcylindrical beam electrode bearingagainst said first',l insulatorringandcoaxial with said cylindrical portion, the outer sure facesoffsaid cylindrical portion and said beam electrodebeing aligned,` acylindrical cathode* sleeveihaving a;concave Aelectron emissive surfacetowards said resonator;` said beam electrodehaving azplura'lityV ofAshort fingers integral therewith extending `along Isaid cathode sleeveand integral @anges intermediate said ngers, said fingers comprising theonly thermal contactib'etween'said cathode sleeve and" said .beamnelectrode, a second' insulator ring fitting'closely around said alignedsurfacesandxpositioningsaid cathode sleeve, said 't beam electrode, andsaid focusing electrode in accurate axial alignment,` a spider spring ibearing against said angesxandbiasing said beam elec trede` towards;said focusing"electrode;` a thinin'- sulating.iringadjacentfsaid.spiderspring, a ring springbearingagainst saidthin insulator ring, and acylindrical retaining member secured to saidmounting member andencompassing said' secondV insulator` ring, said"retaining member`having fingersfb'ent 'over'andbearing against said ring spring.`

CHARLEST. GODDARD.

References Cited 1 in Yth'ele of this patent UNITED STATES PATENTSNumber Name Date 2,239,416'k Ehrenberg Apr. 22l9lll,v 2,414,785'Harrison et al; Jani 21, 194'? 2,452,318 Nergaard !)ct 26, 1948'2,513,296 V 'Ekstrand etai July 4, 1950i

